Display:

$\left(\begin{array}{ccc}1& 0& 0\\ 0& 1& 0\\ 0& 0& 1\end{array}\right)$

Source:

<mrow>
     <mo> ( </mo>
     <mtable>
          <mtr>
               <mtd>
                    <mn>1</mn>
               </mtd>
               <mtd>
                    <mn>0</mn>
               </mtd>
               <mtd>
                    <mn>0</mn>
               </mtd>
          </mtr>
          <mtr>
               <mtd>
                    <mn>0</mn>
               </mtd>
               <mtd>
                    <mn>1</mn>
               </mtd>
               <mtd>
                    <mn>0</mn>
               </mtd>
          </mtr>
          <mtr>
               <mtd>
                    <mn>0</mn>
               </mtd>
               <mtd>
                    <mn>0</mn>
               </mtd>
               <mtd>
                    <mn>1</mn>
               </mtd>
          </mtr>
     </mtable>
     <mo> ) </mo>
</mrow>